It is known that color images may be obtained from imagewise exposed silver halide photographic elements by development with a primary aromatic amine color developing agent in the presence of a color coupler. The oxidized color developing agent formed in the areas of silver halide development couples with the coupler to form a dye. The coupler is normally incorporated in the sensitive photographic element.
It is also known that 5-pyrazolones in which the 4-position of the pyrazolone ring is free, that is having only hydrogen substituents (4-equivalent magenta couplers), can be used as magenta couplers in color photographic elements to provide magenta dye images having useful properties. Examples of such couplers are the 4-equivalents 3-anilino-5-pyrazolone couplers described in, for example, U.S. Pat Nos. 3,519,429, 3,907,571, 3,928,044, 3,935,015 and 4,199,361. However, 4-equivalent 5-pyrazolone couplers have a number of disadvantages, as they require four equivalents of silver to produce each molecule of dye, are sensitive to certain chemical vapors, for example formaldehyde, and have poor dye light and dye dark stability. These drawbacks can be overcome by using so-called 2-equivalent 5-pyrazolone magenta couplers in which a substituent is introduced into the coupling position (4-position) of the coupler and eliminated as a leaving group (coupling-off group or splitting-off groups) during the color development process, thus requiring only two equivalent of silver in order to produce each molecule of dye.
Among coupling-off groups known in this connection are the arylthio groups described, for example, in U.S. Pat. Nos. 3,227,554, 3,701,783, 3,935,015, 4,351,897, 4,413,054, 4,556,630, 4,584,266, 4,740,438, 4,853,319, 4,876,182, 4,900,657, 4,929,540, 4,942,116, 5,250,407, 5,262,292, and 5,256,528; WO 88/04795, 92/18902, and 93/02393; EP 341,204, and GB 1,494,777.
A problem with 2-equivalent magenta couplers is that the magenta image dye formed in the processed photographic elements has rather low fastness to light.
Another disadvantage associated with the 2-equivalent 5-pyrazolone magenta couplers is that they have low pKa values, so that they may be significantly ionized at low pH. Thus, 2-equivalent 5-pyrazolone magenta couplers can exihibit an undesirable non-imagewise dye formation (continued coupling) owing to coupling with developer that is carried over into the bleach solution and oxidized therein. This phenomenon produces undesirable increase in background density (Dmin). Continued coupling also produces unacceptable dye density variability in processed color photographic elements due to variations of bleach pH as the bleach solution becomes seasoned by continuous use.
Thus, there is the need to provide silver halide color photographic elements containing 2-equivalent 5-pyrazolone magenta couplers which exhibit a reduction in the continued coupling phenomenon and form magenta dye images having improved fastness to light.
GB 1,494,777 describes 2-equivalent 1-aryl-3-anilino-4-arylthio-5-pyrazolone magenta couplers wherein the arylthio group contains a ballasting group linked to the aryl group either directly or through a divalent linking group such as an imino, ether, carbonamido, sulfonamido, ureido, imido, carbamoyl or sulfamoyl bond. No examples of couplers having a ballasting group on both the anilino and arylthio groups are disclosed.
U.S. Pat. No. 4,413,054 describes 2-equivalent 1-aryl-3-anilino-4-phenylthio-5-pyrazolone magenta couplers wherein the phenylthio group may be substituted with halogen atoms, alkyl, alkoxy, alkoxycarbonyl, acylamino, sulfonamido, carbamoyl, sulfamolyl, alkylthio, hydroxy, or arly groups. No examples of phenylthio groups having carbamoyl groups in the 2-position with respect to the carbon atom attached to the sulfur atom are reported.
U.S. Pat. Nos. 4,556,630 and 4,584,266 describe 2-equivalent 1-aryl-3-anilino-4-phenylthio-5-pyrazolone magenta couplers wherein the 4-phenylthio group may be substituted with halogen atom, or hydroxy, amino, alkyl, alkoxy, aryl, acylamino, ureido, alkoxycarbonylamino, imido, sulfonamido, sulfamoyl, nitro, alkoxycarbonyl, carbamoyl, acyl, cyano or alkylthio groups. No examples of couplres having a carbamoyl group on the phenylthio group are disclosed.
U.S. Pat. No. 4,900,657 describes 2-equivalent 1-phenyl-3-anilino-4-arylthio-5-pyrazolone magenta couplers wherein the 1-phenyl group has at least 4 Cl atoms and the 4-arylthio group has in ortho position a sulfonamido, carbonamido, ureido, carbamoyl, amino, alkyl or alkoxy group. No examples of couplers having a carbamoyl group on the arylthio group are disclosed.
U.S. Pat. No. 5,256,528 describes 2-equivalent 1-phenyl-3-anilino-4-phenylthio 5-pyrazolone magenta couplers wherein the 4-phenylthio group has in ortho position a halogen atom, or an alkyl, alkoxy, aryloxy, carbamate, sulfonamido, carbonamido, ureido, carbamoyl, sulfamoyl, acyloxy, alkoxycarbonyl, aryloxycarbonyl, amino, or carboxyl group. No examples of couplers having a carbamoyl group on the phenylthio group are disclosed.
WO 92/18902 describes 2-equivalent 1-phenyl-3-anilino-4-phenylthio 5-pyrazolone magenta couplers wherein the ortho position of the phenylthio group is substituted with carbamoyl, alkoxysulfonyl, aryloxysulfonyl, alkysulfovyl, arylsulfonyl, alkoxycarbonyl, aryloxycarbonyl, sulfamoyl, acyloxy, acylamino, nitro, cyano, or amine group, and the sum of the sigma values for substituents on the 1-phenyl and 3-anilino groups is at least 1.3.
EP 510,576 and 529,727 describe the continued coupling of two-equivalent 5-pyrazolone magenta coupler as caused by the low pKa values of said couplers and provide a solution to this adverse phenomenon by combining the two-equivalent 5-pyrazolone magenta coupler with a sulfoxide compound and; respectively, a carbonamide compound and at least one compound selected from the group consisting of anilines and amines.